This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. A "ring" Sagnac interferometry system is utilized to perform digital optical phase conjugation. The system permits the wavefield scattered from a turbid medium to be recorded holographically. Then, a complex-conjugate reconstruction of the wave can be generated by a spatial light modulator and propagated through the sample in the reverse direction. This achieves the effect of reversing the effects of sample scattering. The same system is capable of recording a representation of the transmission matrix of the sample, its linear response to an arbitrary wavefield input. This information, and the flexibility endowed by the degree of control permitted by the SLM, can be used to enhance either the accuracy or the total intensity of the phase-conjugate reconstruction.